1. Field of the Invention
This invention concerns an electrophotographic photoreceptor. More Specifically, it relates to an electrophotographic photoreceptor excellent in ozone resistance and also excellent in stability and durability.
2. Description of the Prior Art
As electrophotographic photoreceptors, inorganic photoconductive substances such as selenium, selenium-tellurium alloy, arsenic selenide or cadmium sulfide have been used generally.
In recent years, studies on the use of organic photoconductive substances for photosensitive layers have become active and laminate photoreceptors comprising a carrier generation layer and a carrier transport layer in which the function of absorbing light and generating charge carriers and the function of transporting generated charge carriers are separated have been deviced, which constitute a main stream of the studies, since they are suitable to mass production and have a possibility of providing materials of high safety. An organic compound having a high carrier generating effect and another organic compound having a carrier transporting effect are combined in the laminate type photoreceptor, to obtain a photoreceptor of high sensitivity, which is put to practical use. Since the carrier transport layer is laminated on the carrier generation layer and since the carrier transport layer usually has only positive hole moving function, the laminate electrophotographic photoreceptor has a sensitivity only when it is charged negatively and it is used under the negatively charged state.
On the other hand, in the electrophotography, the photoreceptor is usually charged by corona discharge. However, it is difficult in the negative corona discharge to attain uniform discharge in the direction of the wire and, thus, it is difficult to obtain uniform charge as compared with positive corona discharge. In addition, selenium-based photoreceptors conventionally used in the prior art work under positive charging, accordingly, an organic photoreceptor that can be used in the positively charged state is also studied with an intention of utilizing the prior art in view of the developer and other peripheral processes used in the system. For instance, there have been proposed and studied for a so-called reverse two-layer photoreceptor in which a carrier transport layer and a carrier generation layer are are laminated in this order on a support, and a dispersion type photoreceptor in which particles of the carrier generating substance are dispersed in the carrier transporting medium. In the reverse two-layer and dispersion type photoreceptor, incident light is absorbed on the surface and the region of generating carriers situates near the surface and it is used under positive charging.
Thus, photoreceptors of several constitutions have been proposed and studied and photoreceptors having excellent charging characteristics and sensitivity have been developed. Electrophotographic photoreceptors are used repeatedly in the system and required to have always constant and stable electrophotographic characteristics throughout the use, but no sufficient stability and durability have yet been obtained at present with any of the constitutions described above. That is, they result in lowering of the potential, increase of the residual potential, change of the sensitivity and the like along with the repeated use to cause reduction of the copy quality and become no more usable. Although the cause for such degradation has not yet been quite clear, there may be considered several factors. Among them, it has been known that oxidative gases such as ozone and nitrogen oxides released from a corona charger give a remarkable damage on the photosensitive layer. The oxidative gases result in chemical changes for the materials in the photosensitive layer to bring about various changes of characteristics. For instance, lowering of the resolution power due to the lowering of the charged potential, increase of the residual potential and the lowering of the surface resistance are recognized, to result in remarkable lowering of the image quality and shorten the life of the photoreceptor.
Against them, it has been considered to effectively exhaust and replace gases near the corona charger thereby avoiding the effect on the photoreceptor, or there has been proposed to prevent degradation by adding an anti-oxidant or a stabilizer to the photosensitive layer. For instance, there have been proposed the addition of an anti-oxidant having a triazine ring and a hindered phenol skelton in the molecule in Japanese Patent Laid-Open (KOKAI) No. 62-105151 (1987), addition of hindered amines in Japanese Patent Laid-Open (KOKAI) Nos. 63-73256 (1988) and 63-18355 (1988), addition of a trialkylamine in Japanese Patent Laid-Open (KOKAI) No. 63-4238 (1988), addition of an aromatic amine in Japanese Patent Laid-Open (KOKAI) No. 63-216055 (1988) and addition of a specific aniline derivative in Japanese Patent Laid-Open (KOKAI) No. 63-96662 (1988).
However, even with such prior art, only insufficient effects can be obtained for practical use at present, for example, no sufficient effect for the ozone resistance can yet be obtained, or electrophotographic characteristics such as the sensitivity or the residual potential are worsened due to the addition of the anti-oxidants as described above.
The present inventors have made an extensive study for the improvement of the ozone resistance of an organic photoreceptor having a carrier generation substance and a carrier transport substance and, as a result, have accomplished the present invention based on the finding that a photoreceptor of excellent electric characteristics with remarkably improved ozone resistance can be obtained by adding a specific amine compound to a photosensitive layer.